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Old 2nd January 2013, 11:20 PM   #451
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Why not have the tda filter caps on the top layer?
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Old 3rd January 2013, 06:22 AM   #452
qusp is offline qusp  Australia
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why not use potato logic for the gates? PO74GO2A

very high quality, lower jitter, lower noise and SMD package

I presume the caps are on the underside to allow them to be still serviceable while the dac chip is in place.
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Old 3rd January 2013, 08:16 AM   #453
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Cmon boys, the layout is rather weird for me - bypasses are weird (i prefer using ground plane as is, and throw the bypass cap as close as possible. To feed the PS trace first thru cap, and then by wide (same width as cap's footprint) trace into IC's pin.

Then the I2S thing... Why those bulky thruholes? Digital is all-SMT world. I still regret i haven't used 0804 in my PCB /but i have my reasons - i've got loads of 1206 in E96 series values. I'll settle on some specific resistor values for 3.3 / 5v logic levels and then go 0804/.

HC02... same thing, why DIP? And if you use just a tiny part of it, why not go with single/dual gates? they are nicier, less substrate bounce as their package is tinier.

Oh, what's characteristic impedance of your digital traces, do they match the characteristic impedance of your source and u.fl connectors/coax?
Do your digital traces have ground cuts underneath the traces?

I've said 13 times "it's release" prior to sending the PCBs to production - and i still got some minor mistakes

Just take some nice book on digital design, like "black magic" of HJ, plus some EMC docs ( EMC Information Centre - The EMC Journal (Free in the UK) is a good place to start, as well as many appnotes on EMC and digital/mixed signal PCB design).

Watch out the current flow. It flows thru trace and always returns back to the place where it came from - it's The Loop, which area you want to keep as small as possible.
Return currents of traces flow under the trace, in the ground plane. If you cut the plane under the trace, the current will have to find other ways around to get back - and they don't care of flowing thru the air, making-up some nasty EMI emissions.
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Old 3rd January 2013, 09:01 AM   #454
qusp is offline qusp  Australia
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thanks, you gave the critic I dont have the investment/interest to give =) MCLK trace should actually be somewhat wider than the others if you can without interfering with the other pins and the TDA pitch allows that.
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Old 3rd January 2013, 09:10 PM   #455
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Quote:
Originally Posted by s3tup View Post
Cmon boys, the layout is rather weird for me - bypasses are weird (i prefer using ground plane as is, and throw the bypass cap as close as possible. To feed the PS trace first thru cap, and then by wide (same width as cap's footprint) trace into IC's pin.

Then the I2S thing... Why those bulky thruholes? Digital is all-SMT world. I still regret i haven't used 0804 in my PCB /but i have my reasons - i've got loads of 1206 in E96 series values. I'll settle on some specific resistor values for 3.3 / 5v logic levels and then go 0804/.

HC02... same thing, why DIP? And if you use just a tiny part of it, why not go with single/dual gates? they are nicier, less substrate bounce as their package is tinier.

Oh, what's characteristic impedance of your digital traces, do they match the characteristic impedance of your source and u.fl connectors/coax?
Do your digital traces have ground cuts underneath the traces?

I've said 13 times "it's release" prior to sending the PCBs to production - and i still got some minor mistakes

Just take some nice book on digital design, like "black magic" of HJ, plus some EMC docs ( EMC Information Centre - The EMC Journal (Free in the UK) is a good place to start, as well as many appnotes on EMC and digital/mixed signal PCB design).

Watch out the current flow. It flows thru trace and always returns back to the place where it came from - it's The Loop, which area you want to keep as small as possible.
Return currents of traces flow under the trace, in the ground plane. If you cut the plane under the trace, the current will have to find other ways around to get back - and they don't care of flowing thru the air, making-up some nasty EMI emissions.

Thanks for the advice. I have made some changes. The through hole was mainly because I am more comfortable with it, and the tda1541a is through hole also. But here we go.

As far as the impedance of the traces, I don't know how to determine that, and don't have the equipment even if I did. But My goal is not really the best ever created. In fact, I was planning on purchasing your board when finished, although last I checked it seamed you were going for a slaved source setup. Mainly I wanted to try a basic universal tda1541a Dac, that is simple to construct and incorporates many of the elements that have been found to improve the sound. And I have never done a digital layout before, and nothing seems available that meet what I'm looking for.

Which is why I appreciate the help, and hopefully the following looks better.

Also, could you explain what you mean by ground cuts underneath the traces.

Thanks,
Chris
Attached Images
File Type: png dac-1-simple-v2.png (43.2 KB, 289 views)
File Type: png dac-1-simple-v2-top.png (694.8 KB, 293 views)
File Type: png dac-1-simple-v2-bot.png (402.3 KB, 284 views)

Last edited by vanofmonks; 3rd January 2013 at 09:12 PM. Reason: Spell my name correctly
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Old 4th January 2013, 01:02 AM   #456
erin is offline erin  Australia
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TDA sounds best with shunt regulators near the pins (TL431). It is so important to good sound with this chip, that there is no point to making a board without it IMO.

Also, I would suggest the thickest possible traces for the LR current output pins.
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Last edited by erin; 4th January 2013 at 01:06 AM.
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Old 4th January 2013, 01:35 AM   #457
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VR 1-5 are tl-431, and the regs for the tda1541 are probably as close as possible. I uploaded a schematic a few comments ago. But it is not fully up to date.
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Old 4th January 2013, 04:11 AM   #458
qusp is offline qusp  Australia
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wouldnt it be better to have the u.fl on the other side of the strip header?
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Old 4th January 2013, 01:07 PM   #459
regal is offline regal  United States
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Quote:
Originally Posted by erin View Post
TDA sounds best with shunt regulators near the pins (TL431). It is so important to good sound with this chip, that there is no point to making a board without it IMO.

Also, I would suggest the thickest possible traces for the LR current output pins.
Is the TL431 really a good choice? If you went smt with potado logic and dropped the TL431's you could have a really small board that could butt right next to salas regs.

As far as the tda cap decoupling yours is the best board I've seen. I don't see and cuts in the ground plan except the ground connects to the caps they aren't the correct ones to use you want pads that have continous contact to the ground plane they are smd caps but you have odd connection to ground, they look like thru hole.

Yours is a slaved source setup too. I think you have outdone all other recent attempts. As far as the trace impedance there are formulas for calculating also terminating the ufl connector with a resistor is important. I bet you can make this simple board the best out there with just a little more research. You can probably find it on a search. I think something like this would be very useful for a lot of us.

There isn't much else out there besides the terrible raindrp china boards and the rb boards have many mistakes.

Thanks for sharing.
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Old 4th January 2013, 01:39 PM   #460
qusp is offline qusp  Australia
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no, with solid ground planes and small SMD, using spoked SMD ground pads is perfectly reasonable, you will find Ian uses these often too, it makes the board much more solderable and at these currents really doesnt have any disadvantage.

to terminate or not... hmm depends, the transport/TX is terminated already and if the connectors are consistent with the impedance, I dont think its so cut and dried that you must terminate every u.fl at both ends

Last edited by qusp; 4th January 2013 at 01:45 PM.
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